Serum albumin is a marker of nutritional and frailty status. This study aimed to assess the association between serum albumin at the time of admission and the risk of acute respiratory failure (ARF) in hospitalized patientsThis cohort study, performed at a tertiary referral hospital, included all hospitalized adult patients from January 2009 to December 2013 who had serum albumin measurement and were not on mechanical ventilation within 24 hours of hospital admission. Serum albumin was stratified into 2.4, 2.5 to 2.9, 3.0 to 3.4, 3.5 to 3.9, 4.0 to 4.4, and ≥4.5 g/dL. Multivariate logistic regression analysis was performed to obtain adjusted odds ratio (OR) of risk of ARF requiring mechanical ventilation based on various admission serum albumin levels.Of 12,719 patients, ARF requiring mechanical ventilation occurred in 1128 (8.9%) during hospitalization. Hypoalbuminemia was associated with increased risk of ARF, in particular when serum albumin was ≤2.4 g/dL. Compared with serum albumin of 4.0-4.4 g/dL, serum albumin ≤2.4 g/dL at admission was associated with 2.38-time higher odds of ARF during hospitalization (OR 2.38, 95% confidence interval [CI] 1.84-3.07). In contrast, elevated serum albumin ≥4.5 g/dL was associated with lower odds of ARF (OR 0.68, 95% CI 0.48-0.97).Admission serum albumin level lower than 3.5 g/dL was associated with a higher risk of ARF requiring mechanical ventilation, whereas elevated serum albumin level at least 4.5 g/dL was associated with a lower risk of ARF. Therefore, admission albumin level at admission might be useful in the prediction of ARF during hospitalization.